A Sierra Leonean surgeon critically ill with Ebola was flown to a Nebraska hospitalfor treatment on Saturday and is sicker than previous patients treated in the U.S., medical officials said.

Dr. Martin Salia, 44, a permanent U.S. resident who caught Ebola working as a surgeon in a Freetown hospital, was stable enough to take a flight from West Africa and arrived at Eppley Airfield in Omaha at 2:45 p.m. local time (3.45 p.m. ET), Nebraska Medical Center said.

Salia was too sick to walk off the plane and was transferred to a waiting ambulance in an isolation unit called an ISOPOD, a device used in the transportation of a potentially infectious patient, a Nebraska Medical Center official said.

“Although the patient’s exact condition won’t be available until doctors here evaluate him after he arrives, information coming from the team caring for him in Sierra Leone indicates he is critically ill — possibly sicker than the first patients successfully treated in the United States,” the hospital in Omaha, Nebraska, said in a statement.

Salia will be the third patient treated for Ebola in the Nebraska hospital’s Biocontainment Unit since the outbreak gained momentum this year in Sierra Leone,Guinea and Liberia.

Salia was chief medical officer at the United Methodist Church’s Kissy Hospital when he was confirmed on Tuesday to have contracted Ebola.

His evacuation was at the request of his wife, a U.S. citizen who lives in Maryland and who has agreed to reimburse the U.S. government for any expense, the U.S. State Department said in a statement.

A medical crew with Phoenix Air examined Salia in Sierra Leone before leaving with him en route to the U.S. on Friday night, the Nebraska hospital said.

According to the latest figures from the World Health Organisation, at least 5,177 people have died in the world’s worst recorded Ebola outbreak.

Most of the victims have been in Sierra Leone, Liberia and Guinea, where already weak healthcare systems have been over-run by the disease. A total of 570 local health workers have been infected, with 324 of these dying.

Salia would be the 10th known case of Ebola in the United States. All but one case was treated successfully treated.

The Nebraska clinic is one of four American hospitals approved by the federal government to treat Ebola.

(Reporting by Katie Knapp Schubert and Umaru Fofana; Additional reporting by Barbara Goldberg in New York; Writing by David Lewis and Victoria Cavaliere; Editing by Elaine Hardcastle and Stephen Powell and Franklin Paul)